1. Field of the Invention
This invention relates to the recovery of glycine and Glauber's Salt (Na.sub.2 SO.sub.4.10H.sub.2 O) from solutions such as the liquor generated in the process of producing glycine.
2. Description of the Prior Art
Typical prior art processes for the recovery of glycine from sodium sulfate solutions are disclosed in U.S. Pat. Nos. 3,904,585 and 3,947,496.
U.S. Pat. No. 3,904,585, the disclosure of which is herein incorporated by reference, discloses a process of recovering glycine or B-alanine from a starting aqueous solution of sodium sulfate and the amino acid having a temperature above about 33.degree. C., a pH of 4.5-8.5, a mole ratio of amino acid to sodium sulfate of about 1-5:1 and containing at least 5% amino acid. The process comprises forming a first slurry without precipitating the amino acid, (the first slurry being a mixture of precipitated sodium sulfate and first mother liquor), by evaporating water from the starting solution while maintaining its temperature within a range (from 60.degree. or 70.degree. C. up to the normal boiling point) effective for preventing the precipitation of the amino acid, separating the first mother liquor from the precipitated sodium sulfate, cooling the separated first mother liquor to a temperature within a range (33.degree.-40.degree. C.) effective for precipitating the amino acid, and separating and recovering the precipitated amino acid.
U.S. Pat. No. 3,947,496, the disclosure of which is herein incorporated by reference, discloses a process for recovering glycine from an aqueous starting solution of glycine and sodium sulfate that is similar to the process of the U.S. Pat. No. 3,904,585. The process comprises cooling the aqueous starting solution to a temperature above about 33.degree. C. so that glycine is precipitated, and separating and recovering the precipitated glycine. Further steps include precipitating anhydrous sodium sulfate by evaporating water from the separated first mother liquor, etc.
The foregoing references use processes where the temperature is specified to be 33.degree. C. or higher so as to avoid the precipitation of sodium sulfate decahydrate with the amino acid. These processes generate waste liquor streams which include a substantial amount of product. Impurities generated in the glycine production process, for example, are removed as a waste purge stream taken from the glycine mother liquor tank. The primary constituents of this stream are glycine, iminodiacetic acid (IDA) monosodium salt, Na.sub.2 SO.sub.4, and water. A typical composition is about 18% glycine, 11% IDA expressed as IDAH.sub.2, 12% Na.sub.2 SO.sub.4, with the balance being water and unidentified organic compounds. Streams such as this have heretofore been discarded.
Other approaches to the recovery of amino acids include U.S. Pat. No. 3,510,575 where glycine is separated from NH.sub.4 Cl, U.S. Pat. No.4,691,054 where amino acids are isolated by ion exchange from systems that are substantially free of inorganic ions (such as sodium sulfate), and U.S. Pat. No. 4,299,978 where the mother liquor after separation of glycine is acidified to isolate IDA bisulfate, and the new mother liquor formed is recycled to the process. Glauber's Salt is not generated.